Certain applications require measuring aspects that are based on the speed of light.
For example, range finding can be carried out using optics. An optical signal is sent. The reflection therefrom is received. The time that it takes to receive the reflection of the optical signal gives an indication of the distance.
The so called lock-in technique uses an encoded temporal pattern as a signal reference. The device locks into the received signal to find the time of receipt. However, noise can mask the temporal pattern.
A lock in photodetector based on charged coupled devices or CCDs has been described in Miagawa and Kanada “CCD based range finding sensor” IEEE Transactions on Electronic Devices, volume 44 pages 1648-1652 1997.
CCDs are well known to have relatively large power consumption.